Metabolix grows plastic (producing) plants

By Jerry W. Kram

Bacteria have been genetically engineered to produce bioplastics for many years, but someday production may be as easy as watching the grass grow. Cambridge, Mass.-based Metabolix Inc. has created a variety of switchgrass that produces significant amounts of polyhydroxybutyrate (PHB) bioplastic in leaf tissues.

The company incorporated multiple genes into the switchgrass genome, resulting in a functional multi-gene pathway in switchgrass. This is significant, the company said, because instead of adding one or two new genes to create a new compound, Metabolix inserted all of the genes necessary to create an entirely new metabolic pathway into the plant. To accomplish that feat, not only does each of the genes have to work properly, but they all have to work together to change sunlight and nutrients into bioplastic.

Metabolix put its new switchgrass varieties to the test in greenhouse trials, which demonstrated that the plants could create significant amounts of PHB bioplastic in their leaves and stems. In fact, the plants produced as much as 3.7 percent of their leaf tissue weight in PHB. The company said it will have to get the plant to produce 5 percent or more to make commercial production viable. "Metabolix has been developing technology to produce PHB polymers in switchgrass for more than seven years," said Oliver Peoples, chief scientific officer for Metabolix. "This result validates the prospect for economic production of PHB polymers in switchgrass and demonstrates for the first time an important tool for enhancing switchgrass for value-added performance as a bioenergy crop."

Metabolix President and Chief Executive Officer Richard Eno said this technology could advance the development of cellulosic biofuels. Adding new products that can be made from cellulosic crops such as switchgrass could allow cellulosic biofuels producers to diversify their income streams, which could also make switchgrass a more lucrative crop for producers to grow.

Metabolix partnered with Archer Daniels Midland Co. in 2007 to create a joint venture called Telles that aims to produce PHB through fermentation marketed under the brand name Mirel. A facility in Clinton, Iowa, will produce 110 million pounds of Mirel PHB per year and is expected to be operational in the second quarter of 2009. According to the companies, Mirel bioplastics differ from other bioplastics in that they have excellent strength and toughness, and can resist heat and hot liquids. Mirel plastic resins can be used in standard plastic applications from lipstick tubes to disposable coffee containers and lids to agricultural mulch.

A detailed scientific paper on this technology, titled "Production of Polyhydroxybutyrate in Switchgrass, a Value-Added Coproduct in an Important Lignocellulosic Biomass Crop," was recently published in Plant Biotechnology Journal.